CA1047724A

CA1047724A - Method of corrugating a web of thin thermoplastic material in continuous production

Info

Publication number: CA1047724A
Application number: CA194,838A
Authority: CA
Inventors: George W. Meek
Original assignee: Carl Munters AB
Current assignee: Carl Munters AB
Priority date: 1973-03-13
Filing date: 1974-03-13
Publication date: 1979-02-06
Also published as: JPS5730650B2; FR2221257A1; SE387574B; GB1466993A; DE2411165B2; BE812245A; BR7401910D0; DE2411165A1; AU6651074A; FR2221257B1; SU656484A3; US3969473A; ES424233A1; JPS49126768A; AR201498A1; IT1005644B

Abstract

ABSTRACT OF THE DISCLOSURE
Method for continuously forming a corrugated web of ther-moplastic material in which the corrugations extend across the web.
The web is first softened by heat and then passed to a molding belt which moves in an endless path while supporting and advancing the web in a longitudinal direction. The molding belt is provided with grooves corresponding to the corrugations in the web. The corru-gations are formed initially by poking the softened web progressive-ly into the grooves without stretching the web to any substantial degree. The thus initially formed corrugations are thereafter drawn into the grooves and retained therein by applying suction to the bottom side of the molding belt.

Description

FIELD OF THE INVENTION
This invention relates to a method of forming a web of thin thermoplastic material with corrugations in a continuous production.
More particularly this invention relates to a method of form-ing a web of thin thermoplastic material with corrugations in a continuous production by heating a web to soft state and thereupon conveying it into crosswise, preferably diagonally extending, gr,ooves in a mould movable along a closed path, which mould is subjected to a pressure differential, preferably a partial vacuum, between its two sides.
THE PRIOR ART
It is known to draw a web of thin sheet material down into

2~ the grooves of the mould by means of a partial vacuum produced at the underside thereof. The reduced pressure thus serves the entire purpose of forming corrugations in the web of material. In using this procedure, the soft web is subjected to a stretching action which can not be avoided, especially as the web, during the for-mation of each corrugation, is forced against the rear ridge ofthe groove as the corrugation is pulled down towards the bottom of the groove. As the tractional force exerted on the soft web varies during the different stages of the formation of the corrugations, .. . ..

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~ ~ 1047724 ~ e degree of stretching will also vary with consequent variations in the thickness of the corrugated web. Thus, it becomes consider-ably weakened in some portions, whereby the corrugated layer of mater-ial as a whole will have a reduced mechanical strength, which is al-ways determined by the weakest place.
Layers or sheets manufactured according to the invention areused primarily for contact bodies or exchanger bodies for two media, one of which may be a liquid, such as water, and the other, a gas, such as air. Examples of such application are cooling towers, mois-tening devices. so-called scrubbers, and similar apparatus. Due to the general uncontrollable weakening in the corrugated layers, such contact bodies or exchanger bodies have a substantially reduced capac-ity of resistance to strains caused by supplied water, precipitation of ice and similar causes.
MAIN OBJECTS OF THE INVENTION
One main object of the invention is to provide an improved method of continuous manufacture of the corrugated web of plastic material by which partial or local weakening of the finished web ef-fectively is avoided.
! 20 Another main object of the invention is to provide a method ~ . .
which combines the continuous manufacture of the corrugated web of plastic material without any partial or local weakening in the final product with a folding over of at least one lateral edge of the web in order to obtain a reinforced web or sheet material.
Still an object of the invention is to provide an apparatus for carrying out the combined method of manufacture in a continuous process.
SU~n~ARY OF THE INVENTION
According to one main feature of the invention, the web of 30 plastic material, after the heat treatment in a first step, is sub-jected to a mechanical force which acts mainly transversely to the lon- :
gitudinal direction of the web and progressively is ir,serted into suc-cessive grooves. The corrugations thus initially formed are thereafter in a second step, while still soft, Einally brought to conform to the --.

contour of the grooves by the pressure differential acting on the web.
In view of the fact that the corrugations are located in the grooves before the pressure differential or the partial vacuum acts on them, the traction forces acting in the longitudinal di-rection of the web become negligible and the final formation of the corrugations can be made without weakening in parts of the corru-gations. The soft thin web can be poken down mechanically while -it is located in the passage between the heating zone and the mould-ing zone where the web loosely hangs down. The web may be fed from -- -the storage roll before the web has become soft in the heating zone.
The method according to the invention can with advantage be ~ ~
combined with a treatment step comprising folding over at least one -~ -of the longitudinally extending edges of the web of material, re-sulting in doubled thickness of the edge which imparts increasedmechanical strength to this part of the web or sheet material which is exposed most to external strains or loads.
The invention includes also an apparatus for carrying out the method. This apparatus comprises guide members for conveying the web of material to be corrugated past a station with heater mem-bers for softening the material and thereafter over a moulding table which moves along an endless path and is provided with grooves cor-responding to the desired corrugations, a space being provided at the underside of the moulding table, which space communicates with a source of partial vacuum. The apparatus is characterized by a forming head arranged between the heating station and the moulding table at the feed-in end for the web of material and driven syn-chronously with said table and provided with vanes or battens in correspondence with the grooves, said forming head being designed to poke the corrugations down into the grooves as a first step be-fore the final moulding thereof is effected by the partial vacuum.
Further objects, features and advantages of the invention will become apparent from the following description of an apparatus ~ -~ , .
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`: -` 10477Z4 for carrying out the method considered in connection with the ac-companying drawings, which form part of this specification and of which:-..
; BRIEF DESCRIPTION OF THE DRAWINGS
, Figs. 1 and 2 are side elevations of the left-hand and the right-hand part of the apparatus, respectively.
Fig. 2a is a sectional view following the line 2a-2a of Fig.
2b.
- Fig. 2b illustrates diagramatically the forming of the cor-gurations.
Fig. 3 is a perspective view of a portion of the apparatus where the folding over of the lateral edges of the web of material is effected.
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~t Fig. 4 is a sectional view following the line IV-IV of Fig.3.
`~ 15 Figs. 5 and 6 are perspective views of a portion of a cor-~ rugated web of material and represented in various degrees of enlarge-!' ~ ment.

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Referring now to the drawings, the illustrated apparatus com-~20 prises the following main parts: a station A for folding over the lateral edges of the web of material; a station B for heating the web; and a station C for the forming of the web with corrugations.
! The frame 10 of the apparatus comprises a table 12, in which ;-is journalled a storage roll 14 of a web of thin thermoplastic mater-ial-such as polystyrene, polyvinyl chloride or some other plastic material. The table may suitably also carry a spare roll 141, so that a fresh roll may be brought into the production line in the simplest way. The web 16 of material is guided about two guide pul-leys 18, 20 in upward direction to the edge folding station A, through

3~ which it preferably moves in a vertical direction. This station is equipped with two rollers 22, 24, of which the roller 22 has a cyl-indrical central portion 26 and two end discs 28. The latter have an inner plane surface 29 which merges with a conical surface 30.
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, ~ 0477Z4 The second roller 24 has a cylindrical contour which matches the cylindrical central portion 26 of the roller 22, so as to provide a gap between the ends of the portion 26 and the disc surfaces 29 said gap slightly exceeding the thickness of the web of material.
The length of the cylinders 24, 26 corresponds to the desired final width of the finally corrugated web of material. Since this length is shorter than the width of the web, the lateral edges 32 of the web will be folded at an angle of 90 between the cylinder 24 and the end discs 28 of the cylinder 22. During the continued move- i ment of the web of material, these portions 32 folded 90 will be further folded by guide rails 34 an additional 90 inwardly towards ~--the web, which thereupon passes between two driving rollers 36 ad-jacent the upper end of the edge folding station A. Thus, the web is drawn upwards from the storage roll 14 through said station by the rollers 36 bearing against one another. The web still has room temperature and therefore maximum mechanical strength.
Thereafter, the web is guided approximately horizontally to that part of the frame 10 which houses the he~ting station B.
In the upper part of the frame a feeler roller 38 may be arranged, which is supported by arms 49 mounted pivotably about journals 42 and actuated by traction springs 44. This roller controls the driv-ing rollers 36 so that the web will always describe a loosely sag-ging curve between the driving rollers and the station B.
After having passed over a guide pulley 46, the web 16 is moved vertically downwards along a row of electrical heaters 48.
A reflector 50 which accumulates radiated heat may be located op-posite to the heaters, so that the rear side of the web will also be heated. The web softens now to such a degree that it becomes mouldable. Since the lateral edges 32 have been folder over, the web here has double thickness. For this reason, said edgesJ e.g., below the heaters 38, may be further heated by an additional heat-ing device 52. This device may consist of tubes through which hot air is supplied.

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The web 16 of material continues thereupon over one or several guide rollers to the corrugating station C (Fig. 2), where it moves in a substantially horizontal direction. This station comprises a moulding table 56 which follows an endless path between two sprockets 58, 60 mounted rotatably about shafts 62 and 64, re-spectively, in the stationary frame 10. The moulding table is com- ~-~
posed of sheet metal parts or plates 66 (Figs. 2a, 2b) which are provided with grooves 67 corresponding to the corrugations with which the web of material is to be formed. The plates form in the upper part of the moulding table 56 an even, coherent moulding track, the grooves 67 of which are positioned diagonally, which means that they form an oblique angle to the lateral edges of the web. The table may in this connection be made as is disclosed in the Canadian patent specification No. 858,24~ or U.S. patent ap-plication No. 257,841, filed May 30, 1972 (now U.S. Patent No.
3,819,453 dated June 25, 1974), whicharereferred to for a more de-tailed description of the structural reatures and mode of operation of the table. The plates 66 may have a plane surface 88 opposite to the grooves 67. After the adjacent horizontally located plates have passed over the upper part of the table, they are returned to the feed-in end of the moulding table at the lower portion of the endless table as is disclosed by said patents.
Provided at the feed-in end is a corrugating or forming head 68 equipped with vanes or battens which are parallel to the diagonally positioned grooves in the moulding track and driven syn-chronously therewith so that one batten or vane each time moves downwards into a groove in the table and during this movement carries~
along a portion of the web 16 of the material. The forming head 68 may in this connection be formed as is disclosed in said patents 3~ or in U.S. Patent No. 3,682,747. In Fig. 2b, three of the vanes or battens of the forming head are denoted 90a, 90b and 90c. They rotate about an axis 92 in the direction 94 of rotation and syn-10~77;4 ~
chronously with the direction 96 of movement of the moulding table 56.
` Between the guide pulley 54 and the forming head 68, the ; material web 16 hangs down loosely and no traction and hence no stretching of the web will occur when it is progressively broken down into the successive grooves of the moulding table by the battens of the forming head 68. Thus, when the soft web 16 begins to be po~ed downwards into a groove 67 by the vane 90b, it is brought in-to overlying engagement with the front ridge of the groove, viewed in the direction of movement 96 of the table, without any detri-mental sliding movement, but is positioned above the next followingridge behind the engaged groove. The poki`ng down of the web into the groove can be started by the vane 90c and is completed by the vane 90a, as shown in Fig. 2b. Since the plates 66 of the moulding table 56 are cold when the latter arrive beneath the forming heat 68, it is important not to cool the web of material and not to im-part thereto a non-uniform temperature by too early a partial con-tact with the plates. ,-Thus, when a corrugation has just been formed in a groove `
and follows substantially the contour thereof, the corrugation will be subjected at the underside to a partial vacuum which is produced in a vacuum box 70 below the upper part of the moulding table. This 1 ~ -box communicates through a duct 72 with a vacuum source. Since the web of material is heated and soft, it can now, without being sub-jected to any detrimental stretching force in the longitudinal di-rection, be moulded exactly to the shape of the grooves. As willbe seen from Figs. 2a and 2b, the plates of the mould have perfor- ~ -ations 74, through which the partial vacuum reaches the web of plastic sheet material. ~-Thereafter, the web of sheet material continues with the newly formed corrugations lying in the grooves 67 of the moulding table 56 while the moulding table passes through another vacuum zone defined by a box 76 and provided with a duct 78 communicating with a vacuum source. The reduced pressure in the second zone may be less than in the first one, and the second zone serves also for cool-ing the corrugated web of material so that this regains its original hard condition.
Fig. 2, shows a guide roller 80 at the end of the moulding table, from which roller the finally corrugated web leaves to be severed into pieces of desired length.
The shape of the final plastic sheet is best seen in Figs. 5 and 6. It has diagonally extending corrugations 82 which may have a height of between 5 mms and 50 mms, preferably between 12 ~ms and 25 mms, and smaller or shallower grooves 84 which extend transversely to the longitudinal direction of the corrugations between the grooves :~-and ridges thereof. These smaller or shallower grooves have for their purpose to reinforce the sheet and to enhance the dispersion of the liquid, e.g., when the finished contact body in a cooling tower is flushed-with water.
Along their edges, the sheets of plastic material have folded-over portions 32 which to a substantial degree contribute increased mechanical strength t~ the sheets and, consequently, to the contact body manufactured therefrom. For this purpose, the sheets are assembled one above the other, as is disclosed, by way of example, in the U.S.
Patent No. 3,415,502, with the bigger corrugations 32 crossing one -`
another in adjacent layers. The sheets may have a thickness of some tenth or several tenths of one millimeter, and, thus, their thickness ~`
at the edge portions 32 will be double the latter. In order to prevent the portion;~f the sheets between their thickened edge portions coming into full contact with one another, the lateral edges of the moulding plates are made as shown in Fig. 2a, with the ridge summits proper provided with recesses 86 which fit the width of the folded-over por-tions 32. Thus, the outwardly facing ridges of the corrugations dur-int the moulding of the soft web will be located in the same plane SQ
that they abut against the ridges of the adjacent layers under the same conditions in their entire longitudinal extension. In this manner A

uniformity of thickness of the sheets throughout a pack formed by the sheets will be insured. The layers or sheets are inter-connected at the places of contact between the ridges of adjacent layers or sheets. In this connection, it is essential that the ridges are located in the same plane so that the number of places ` of contact reaches a maximum value. The folded-in edge portions 32 need not be glued together in the main portion of the web.
ALTERNATIVE EMBODIMENT
According to an alternative embodiment, the edge folding ~ -station A is located behind the heating station B and thus ahead of the corrugations forming station C. The web of material will -thus be soft when the folding over of its lateral edges is effected.-While one more or less specific embodiment of the inven-tion has been shown and described, it is to be understood that this is for the purpose of illustration only, and that the invention is ~-not to be limited thereby, but its scope is to be determined by the appe~de~ claims.

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Claims

THE EMBODIMENTS OF THE INVENTION FOR WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED, ARE DEFINED AS FOLLOWS:

1. In a method of forming a web of thin thermoplastic mater-ial with corrugations in a continuous production by heating the web to soft state and thereupon conveying it downwards into ob-liquely extending grooves in a mould movable along a closed path which mould is subjected to a pressure difference, between its two sides, characterized in that the web after the heat treatment in a subsequent first step by means of a mechanical force acting main-ly transversely to the longitudinal direction of the web success-ively is conveyed down into one groove after the other groove and that the corrugations preliminarily formed in this way thereafter in another step while still being soft are forced finally to fit to the contour of the grooves by the pressure difference acting on the web.

2. The method of claim 1, characterized in that the grooves extend diagonally to the lateral edges of the web.

3. The method of claim 1, characterized in that the pressure difference is a partial vacuum.

4. The method of claim 1, further characterized in that the web of material is conveyed from a storage roller to the corru-gation forming steps by means of a tractive force which is applied prior to the heat treatment step.

5. The method of claim 2, further characterized in that the heat treatment step is carried out while the web moves in downward direction in radiation contact with heater members.

6. The method of claim 1, further characterized in that the web of material in the grooves of the moulding track is subjected to a greater partial vacuum immediately after the first corrugat-ing step than when it thereafter is retained in the grooves for cooling and therewith stabilization of the corrugations.

7. The method of claim 1, further characterized in that the web of material prior to the corrugations forming step is folded over with a portion along at least one of its lateral edges.

8. The method of claim 7, characterized in that the web of material is formed with the longitudinally extending overfold of the edge while the web from the store roller is subjected to a tractive force.

9. The method of claim 7, characterized in that the longi-tudinal edges of the web are folded over in the same direction as the web during the corrugating operation so that the folded-over edge portion becomes turned downwards towards the moulding table.

10. An apparatus for carrying out the method of claim 1 for forming a web of thermoplastic material with corrugations and com-prising guide members for conveying said web past a heating station equipped with heater members for softening the material and there-upon over a moulding table movable along an endless path and pro-vided with grooves corresponding to the desired corrugations, a space being provided at the underside of the moulding table and in communication with a source for partial vacuum, characterized by a corrugations forming head arranged between the heating station and the moulding table at the inlet side of the latter for the web of material and driven synchronously with said table and provided with vanes or battens in correspondence to the grooves, said cor-rugations forming head being devised in a first step to take cor-rugations down into the grooves before the final moulding thereof is effected by the partial vacuum.

11. The apparatus of claim 10, further characterized by an edge folding station arranged ahead of the corrugations forming station and provided with roller and guide members for folding over at least one of the lateral edges of the web of material.

12. The apparatus of claim 11, characterized by the moulding table consisting of plates provided with grooves, the ridges be-tween said grooves being at the top side and at the end edges formed with recesses having a depth and a breadth adapted to the folded-over edges of the web of material.

13. The apparatus of Claim 10, characterized by the heater members extending in vertical direction and guide members adapted to move the web of material substantially vertically in downward direction past said members before said web is folded and hit by the vanes of the corrugations forming head.

14. The method of continuously forming a corrugated web from thermoplastic thin sheet material which is rendered relatively weak when heated, the corrugations extending at an oblique angle to the side edges of the web, said method comprising:
a) moving the web through a heating zone to soften the thermoplastic material into moldable condition;
b) folding over at least one of the lateral edge portions to produce a thickened edge to reinforce the softened web;
c) introducing the softened web in depending slack condition to a continuously moving longitudinal corrugating zone comprising a series of diagonal ridges and grooves for engaging and advancing the web without any substantial stretching thereof progressively into successive grooves while maintaining the introductory portion of the web in slack condition;
d) forming the corrugations initially by mechanically de-pressing the softened advancing web without any substantial stretch-ing thereof progressively into successive grooves while maintaining the introductory portion of the web in slack condition;
e) applying suction beneath the thus initially formed cor-rugations to draw them against the surfaces of the grooves and to harden and set the thus completed corrugations; and f) forming a plurality of ribs in said corrugations by drawing the web against corresponding ridges in the corrugating zone in the suction applying step.